youse guys are always jumping on thee ebay interwebz scammers selling copies. With a certificate or print documentation it gives very clear info on paper, size, print method etc, and if customers were aware, or a court had the doc, it would be harder to pass off fakes as real and easier to nail the fuckerz.
In the world of prints, when the prices climb into the thousands, it's one more thing to help prove the piece is not a fake, and an easy reference to find cheaters.
I did have an interesting exchange with an artist one time, which caused us to change the name of the certificate we supply from Certificate of Authenticity to Print Documentation. She made the point she doesn't need a piece of paper to make her art 'authentic'. the wording smacks of Bradford Exchange collector plates and offset 'Limited Edition' runs in the 10s of thousands.